1. Field of the Invention
The present invention relates to a method of fabricating a composite polishing pad for a chemical mechanical polishing process.
2. Description of the Prior Art
Chemical mechanical polishing (CMP) is a method of polishing materials, such as a semiconductor wafer, to a high degree of planarity and uniformity. The process is used to planarize a semiconductor wafer prior to the fabrication of microelectronic circuitry thereon, and is also used to remove high-elevation features created during the fabrication of the microelectronic circuitry on the surface of the semiconductor wafer.
Please refer to FIG. 1. FIG. 1 is of a cross-sectional diagram of a semiconductor wafer 10. The semiconductor wafer 10 comprises a substrate 12, a conductive layer 14 positioned on the surface of the substrate 12 and a dielectric layer 16 positioned on the surface of the substrate 12. The dielectric layer 16 covers the conductive layer 14. Please refer to FIG. 2. FIG. 2 is of a perspective view of a chemical mechanical polishing apparatus 20. The chemical mechanical polishing apparatus 20 comprises a polishing table 22, a polishing pad 24 set on the polishing table 22, a holder 28 for pressing the semiconductor wafer 10 onto the polishing pad 24, a slurry supply apparatus 30 for supplying a slurry to polish the semiconductor wafer 10, and a conditioner 32 to control the distribution of the slurry on the polishing pad and to remove polished material that is formed during the polishing process.
Please refer to FIG. 3 and FIG. 4. FIG. 3 is a top view of the polishing pad 24, and FIG. 4 is a cross-sectional diagram of the polishing pad according to the prior art. The polishing pad 24 comprises three concentric circular grooves 26. The slurry drops from the slurry supply apparatus 30 to the surface of the polishing pad 24 and flows along the concentric circular grooves 26 so as to distribute the slurry over the surface of the polishing pad.
According to the prior art, the semiconductor wafer 10 is set in the holder 28 before performing the chemical mechanical polishing process. The back surface of the semiconductor wafer 10 is held by the holder 28 and the front surface of the semiconductor wafer 10 is pressed onto the surface of the polishing pad 24. During the chemical mechanical polishing process, the holder 28 rotates counterclockwise and moves to-and-fro, and the polishing table 22 also rotates counterclockwise. The relative motion of the semiconductor wafer 10 with the polishing pad 24 polishes the front surface of the semiconductor wafer 10. The surface of the semiconductor wafer 10 becomes globally planar after the chemical mechanical polishing process, as shown in FIG. 5.
Generally speaking, the polishing pads used in CMP of metal wire comprise hard (for example: IC-1000) and soft (for example: POLITEX) polishing pads. The former provides fast removal rate and great planarization effect, but the scratch problems isoccured. The latter can prevent scratch problems and provide a fine polishing effect and good cleaning performance, but the dishing problem of aluminum wire is induced. Therefore, in the prior CMP hard polishing pad is first used to polish the surface of the semiconductor wafer and then a soft polishing pad is used for further polishing so as to complete the planarization process. Two polishing processes are necessary to performed respectively, so both high time cost and consumption cost of polishing pads are required incurred resulting in a low efficiency of in the CMP.
It is therefore a primary objective of the present invention to provide a method of fabricating composite polishing pads used in chemical-mechanical process to solve the above-mentioned problems.
The present invention provides a method of fabricating a composite polishing pad. The method first provides a first polishing pad comprising a glue layer on a surface of the first polishing pad and a plurality of hard polishing materials positioned on the glue layer. Then portions of the first polishing pad are punched off to remove portions of the hard polishing material positioned on the surface of the first polishing pad so as to form a plurality of holes penetrating the first polishing pad. Thereafter, a second polishing pad comprising a glue layer on a surface of the second polishing pad is provided, and a plurality of soft polishing materials adhere to the glue layer. Then portions of the soft polishing material positioned on the surface of the second polishing pad are removed while retaining the glue layer, and the soft polishing material retained on the surface of the second polishing pad completely matches the holes formed in the first polishing pad. Finally, the first polishing pad is stuck on the surface of the second polishing pad so as to form a composite polishing pad comprising a pattern formed by the hard and soft polishing materials on the surface of the composite polishing pad.
The polishing pad fabricated by the present invention comprises a pattern formed by the hard and soft polishing materials on the surface of the polishing pad, so the composite polishing pad simultaneously providesa good removal rate and a great polishing effect. Only one polishing process is required to complete the planarization process, so the time and cost of the chemical-mechanical process is reduced.